1. Field of the Invention
This invention relates in general to heating systems for use with the reaction chambers of chemical vapor deposition equipment, and more particularly to a heating system for use with a horizontal gas flow reaction chamber having rotatable susceptor for supporting a single substrate. 2. Discussion of the Related Art
In the art of manufacturing semiconductor devices, it has long been a practice to employ chemical vapor deposition equipment for depositing various materials, on substrates at high temperatures. Basically, chemical vapor deposition equipment includes a reaction chamber which is configured for containing and controlling the flow of a reactant and carrier gas therethrough. A base, which is commonly referred to in the art as a "susceptor", is located in the reaction chamber for supporting the substrates upon which the material is to be deposited and the reaction chamber, the susceptor and the substrate are heated to a desired reaction temperature.
A particular type of prior art structure is disclosed in U.S. Pat. No. 3,836,751 by Emmett R. Anderson which issued on Sept. 17, 1974. In the Anderson patent, a slab-like susceptor is fixedly supported in a horizontally disposed reaction chamber for supporting a multiplicity of substrates, or wafers. A first radiant heat source is located above the reaction chamber and includes a plurality of elongated radiant heating elements which are disposed in parallel relationship with each other so as to lie along one horizontal axis above the reaction chamber. A second radiant heat source is located below the reaction chamber and similarly includes a plurality of elongated radiant heating elements which lie along a horizontal axis which is below the reaction chamber and is transverse to the axis of the first radiant heat source. Thermal sensors are located in the fixed planar susceptor for monitoring the temperatures in various regions of the susceptor with the regions being disposed along angularly displaced axes which coincide with the axes of the first and second radiant heating sources but are located within the reaction chamber. The thermal sensors produce signals indicative of the temperatures sensed in their respective regions and in conjunction with appropriate circuits and controls, adjust the temperatures in the various regions to produce a substantially flat temperature profile in the susceptor.
While simultaneous deposition of materials on a multiplicity of substrates is desirable from a manufacturing standpoint, it has some drawbacks from a quality standpoint.
The first problem associated with multi-substrate processing in general, and with the structure of the prior art patent discussed above in particular, relates to the carrier gas which contains the atoms of the deposition materials. As the gas, which may be referred to as a reactant gas, flows over the surfaces of the substrate and the susceptor, deposition of the materials results in changes in the concentration of the deposition materials in the carrier gas. Consequently, as the reactant gas flows across or over the length of these relatively large susceptors, across each individual substrate and across a multiplicity of such substrates, different rates of growth of the deposited layer of material have been found. A second problem is that of temperature control which is critical at the elevated temperatures needed for proper deposition. It is difficult, if not impossibe, to control the temperature within the critical tolerances at all the desired locations within the relatively large reaction chambers. This results in different deposition layer thicknesses from one substrate to another, and can even produce varying thickness within the individual substrates. Still another problem is contamination which can result from various factors such as the handling techniques used to load and unload the substrates, the reactant and carrier gas, and indeed from the reaction chamber itself. The reactant gas not only deposits the deposition material on the substrate, but also on the walls of the reaction chamber. In the relatively large reaction chambers required for multi-substrate processing, the unwanted wall deposits can be inadvertently incorporated into the layers being deposited on the substrates.
These problems and drawbacks, as well as other factors, all contribute to significant problems as the semiconductor devices and the uses to which they are put become more sophisticated. As a result, many changes and improvements have been made in the equipment that is used to simultaneously process a multiplicity of substrates. For example, some equipment manufactuers are now using automated loading and off-loading devices to eliminate, or at least substantially reduce, contamination resulting from human handling. Obviously this and other things which are being done to improve the simultaneous multi-substrate processing techniques have helped. However, there are practical limits which many feel will ultimately make the simultaneous multi-substrate processing techniques unacceptable or at least undersirable. One of the limitations is that of the equipment being adaptable for handling larger diameter substrates. The economics of larger diameter substrates are causing many manufactures of semiconductor devices to use larger substrates. However, increasing the size of the substrate is causing some problems with regard to temperature differentials across the substrate, decreasing concentrations of the deposition materials as it is carried across the substrate, and the like.
Therefore, steps are being taken now by some equipment manufacturers to make suitable single substrate processing equipment which is significantly simpler in so far as controlling the various factors involved in chemical vapor deposition. Single substrate chemical vapor deposition equipment becomes inherently more desirable than multi-substrate equipment as the manufacturers of semiconductor devices change to larger substrates, i.e. 6 to 8 inches in diameter or even larger. One important consideration is the cost at risk when processing one substrate as opposed to the simultaneous multi-substrate processing. That is, if something goes wrong, the monetary loss is far less with one substrate that it is with a plurality of substrates.
In commonly owned copending U.S. patent applications: Ser. No. 032,474, filed on Mar. 31, 1987, entitled A ROTATABLE SUBSTRATE SUPPORTING MECHANISM WITH HEAT SENSING DEVICE FOR USE IN CHEMICAL VAPOR DEPOSITION EQUIPMENT; Ser. No. 148,630, filed on May 11, 1987, entitled WAFER HANDLING SYSTEM WITH BERNOULLI PICK-UP; Ser. No. 065945, filed on June 24, 1987 entiltled IMPROVED REACTION CHAMBERS FOR CVD SYSTEMS; each of which is incorporated herein by reference, a new and improved single substrate processing system is disclosed. To the best of our knowledge, no prior art heating system exists or has been devised which is suitable for use in the processing system disclosed in our copending U.S. patent applications.